The invention relates to catalyst systems that include triple-decker bimetallic complexes having a delocalized dianionic ligand. The catalysts are useful for polymerizing olefins.
While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry""s future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they often produce polymers with improved physical properties.
Since the mid-1980s, scientists have become increasingly interested in bimetallic metallocenes, and in particular, how two metal centers communicate with each other via electronic and through-space interactions (see, e.g., Reddy et al. Organometallics 8 (1989) 2107). Cooperative effects are most likely when the two metal centers are electronically coupled through a conjugated pi-electron system. Ultimately, understanding cooperative effects should let polyolefin manufacturers fine-tune polymer properties by varying catalyst structure.
U.S. Pat. No. 6,414,162 describes bimetallic complexes that derive from dianionic indenoindolyl ligands. These complexes can include two metals bonded to the dianionic indenoindolyl ligand. While one of the anions is delocalized and provides pi bonding to a metal, the other is on the nitrogen atom and provides sigma bonding to the second metal. Pending application Ser. No. 10/308,842, filed Dec. 3, 2002, discloses a bimetallic complex with two linked indenoindolyl groups.
Triple-decker complexes, where two metals have a ligand between them that can provide pi bonding, have been known since the late 1970s (see, e.g., J. Am. Chem. Soc. 98 (1976) 3219; J. Am. Chem. Soc. 100 (1978) 999; J. Am. Chem. Soc. 100 (1978) 7429 and Angew. Chem., Int. Ed. Engl. 16 (1977) 1), but there has been no indication that these complexes might be suitable for polymerizing olefins.
Delocalized dianionic ligands are known. In J. Am. Chem. Soc. 122 (2000) 5278, a series of various porphyrins are synthesized. Trimethylenemethane based ligands have been used (J. Am. Chem. Soc. 119 (1997) 343) to prepare monometallic zirconium complexes and it was demonstrated that these complexes could be used to polymerize ethylene. Other delocalized dianionic ligands are reported in J. Am. Chem. Soc. 122 (2000) 5278; J. Am. Chem. Soc. 119 (1997) 343; J. Am. Chem. Soc. 82 (1960) 3784; J. Chem. Soc. Part B (1971) 904; J. Am. Chem. Soc. 87 (1965) 128; ibid., 5508 and Chem. Ber. 117(1984) 1069.
Despite the considerable work that has been done in the area of olefin polymerization, there is a need for improved catalysts. Because of the wide variety of polyolefin end uses, there is also a need for catalysts that can be easily modified to give polyolefins with different property profiles.
The invention relates to catalysts which comprise an activator and a triple-decker bimetallic complex. The complex includes two Group 3-10 transition metals and a delocalized dianionic ligand pi-bonded to each of the metals. Finally, the complex includes two or more ancillary ligands bonded to each metal that satisfy the valence of the metals.
Catalysts of the invention are versatile. The use of two metals gives an extra dimension for modification of the catalysts. The behavior of the catalysts can be modified by choice of each metal, by the choice of the dianionic ligand or by choice of the ancillary ligands. The invention provides a new way to make a large variety of catalyst systems. As end uses continue to evolve that require new and different polyolefins, it is valuable to have a catalyst system that can be easily modified.